In many applications such as in sports, police work, and in industry it is frequently important to use a protective shield to avoid injury to certain portions of the human body. The head may be protected with a rigid, padded helmet but some areas of the body, for example, the rib cage, must be protected with a flexible material. For example, a football player cannot use a rigid rib cage protector because it would restrict movement and because the rigid protector itself could cause injury if it received an impact from below and were driven, for example, into the player's armpit.
In addition to being flexible, a protective shield is desirably light in weight, previous to air so that the areas beneath it can be ventilated, and not deteriorated by water or persperation. In the past such protective shields have largely been made of foam elastomer. Foam is merely padding which cushions the impact and spreads it over a slightly larger area but it does little to absorb much energy. Foam is very bulky for the amount of protection it affords and it is just as yielding in the direction of absorbing impact as it is in any other direction. Foam absorbs shock equally in all directions and it is equally flexible in all directions. Thus, only a thin, too-flexible and relatively ineffective layer protects against impacts that are perpendicular to the plane of the body, while a wide, too-stiff layer inhibits the movement of the arm and chest of a foam chest protector. Increasing the impact absorbing qualities of a foam body shield necessarily requires making the entire shield thicker, less flexible, more bulky and more difficult to ventilate. Although hard shells placed over foam pads tend to spread impacts over a wider area, as set forth above, the hard shells themselves can cause injuries if the impact is not normal to the thickness of the pad.